The semiconductor integrated circuit (IC) industry has experienced rapid growth. Technological advances in IC materials and design have produced generations of ICs where each generation has smaller and more complex circuits than the previous generation. In the course of IC evolution, functional density (i.e., the number of interconnected devices per chip area) has generally increased while geometry size (i.e., the smallest component (or line) that can be created using a fabrication process) has decreased. This scaling down process generally provides benefits by increasing production efficiency and lowering associated costs. Such scaling down has also increased the complexity of processing and manufacturing ICs and, for these advances to be realized, similar developments in IC processing and manufacturing are needed.
For example, higher resolution lithography processes, such as extreme ultraviolet (EUV) lithography processes, are implemented to meet size constraints approaching critical dimension tolerances of 32 nm technology nodes and below. EUV lithography uses a reflective mask (also referred to as a reticle) to transfer a pattern of a layer of an integrated circuit device to a wafer. An exemplary reflective mask is a phase shift mask, which typically includes a patterned absorption layer disposed on a reflective multilayer coating (multi-layered mirror stack), where the patterned absorption layer defines the pattern of the layer of the integrated circuit device in a mask image region of the phase shift mask. Conventional EUV lithography tools undesirably project EUV radiation onto a portion of the phase shift mask outside the mask image region of the phase shift mask, resulting in undesired exposure or overexposure of portions of the exposed wafer. Such undesired exposure (or overexposure) leads to reduced aerial image contrast in the patterns printed on the exposed wafer. Accordingly, although existing EUV masks and methods of manufacturing EUV masks have been generally adequate for their intended purposes, they have not been entirely satisfactory in all respects.